Planetary Spectra
EXOPLANET ALBEDO SPECTRA AND COLORS AS A FUNCTION OF PLANET PHASE, SEPARATION, AND METALLICITY - Kerri L. Cahoy, Mark S. Marley, and Jonathan J. Fortney (see also Geometric Astrology) "The original spectral data from Karkoschka (1994) are binned down to resolution R= λ/Δλ = 5 and R = 15. Even in the R = 5 spectra, one can distinguish between the ice giants (Neptune, Uranus) and the gas giants (Jupiter, Saturn). The ice giants are brightest in the blue and get darker in the red, and the gas giants are not as bright in the blue, due partly to the effects of photochemical products (which we do not model here), but are brighter mid-band and in the red. An important goal of our study is to understand the extent to which such distinctions hold in general for exoplanets and how the phase at which they are observed affects the colors." Ideas Modelling Example Cahoy et. al. use a 'one-dimensional iterative radiative–convective atmosphere model' to describe the radiative transfer and hence final reflected spectra of the planets illuminated and observed. The model takes into account chemical abundances in the atmosphere and even the state of matter they exist in: "The chemistry calculations include "rainout," where refractory species are depleted from the atmosphere due to their condensation into cloud decks", noting that this is often necessary "The spectra of both brown dwarfs and our solar system's giant planets can only be reproduced when chemistry calculations incorporate this process". Section 3.2.5 notes that previous methods were able to show how the intensity '''of planetary spectra changed with phase angle (i.e. geometry) but not how the actual '''spectrum itself changed, which they were able to model by expanding greatly on the existing approaches, using an N-layer planar model of reflective surfaces for the atmosphere and in depth integrative analysis of the scattering effects. These planes are then reconstructed for many points on the surface of the spherical planets to simulate a curved model, integration over the whole surface then gives the final reflectance spectrum. Alternative The above is great for capturing the true complexity of the model for comparison to real data. However, for astrological purposes this might be way overboard. Instead we would really just want to capture the shifts in frequency and intensity of the spectrum at different phases (different geocentric positions in the Zodiac) and perhaps see how they correspond to the astrological wisdom of what positions are considered positive or detrimental for each planet. For example, one might find that the spectrum of Mars is most blue-shifted when it is in Aries and most red-shifted when it is in Scorpio, the two signs it classically was considered to 'rule' and hence feel comfortable in. A simple model would be nice here, one that could be adjusted later for better detail and accuracy but that captures the basics to a fair extent. The Schockley-Queisser model for Solar Cells would be a fairly reasonable blueprint for such a simple, yet useful spectral model. One could model each planet's spectrum on a known albedo function, then calculate the shifts using the geometry? The benefits of such a simple model would be allowing the cumulative effects of multiple planets reflecting not only the primary light of the sun, but also reflecting each other's reflected signals. Orientation However, the above models so far only take into account effects that average over the surface of the planet illuminated. An alternative may be that the orientation of the planet is actually highly significant! This may be most obvious in the case of planet's with abnormal axial tilts, such as Uranus and Pluto, both of which have tilts closer to 90 degrees than 0' or 180' (like Venus). This means that they experience extreme seasonal changes between their poles throughout their very long planetary years and hence the reflectance surface also experiences drastic changes in its properties throughout the orbit. Furthermore, the radial velocity of the surface will change depending on whether the light is reflected off an equatorial surface or a polar surface, although the radial Doppler shift may be negligible compared to other shifts.Category:Geometric Astrology Category:Light Category:Planets